DescriptionAbavorana nazgul is a medium-sized, robust frog with an adult male snout-vent length range of 42.1 - 50.0 mm. A single female specimen had a snout-vent length of 52.8 mm. The head is longer than it is wide, and the snout is relatively short (being wider than it is long), slightly rounded, concave on the dorsal view, and protrudes beyond the lower jaw. The nostrils open laterally, just beneath the canthus, and are found closer to the rostrum than to the eyes. The canthus rostralis is distinct. The lore is vertical and the interorbital region is flat. The interorbital distance is narrower than the snout width, but longer than the snout length. The eyes are large, slightly protrude in the dorsal view, and have circular pupils. The tympanum is round, distinct, and has the same horizontal diameter as the eye. Adult males lack vocal sacs. The skin on the dorsum, snout, limbs, throat, abdomen, and flanks is smooth or finely shagreened. The dorsolateral and tympanic folds are absent; only a weak rictal ridge is present. Vomerine teeth are present, but small and indistinct. The tongue is long, broad towards the back with a central terminal notch, and free at the posterior third (Quah et al. 2017).

The forelimbs are relatively long and slender, and the fingers lack webbing. The fingertips are expanded into small disks with circummarginal grooves. The relative length of fingers is: III > I > IV > II. Nuptial pads are absent on males. Prominent and opaque subarticular tubercles are present – one each on digits I and II, and two each on digits III and IV; the second subarticular tubercle on digits III and IV are indistinct. Also present is a large inner metacarpal tubercle, a slightly smaller outer metacarpal, and palmar tubercles; these tubercles are oval and translucent. The hindlimbs are also long and slender, with the tibia being slightly longer than the femur. The toes are webbed. The webbing formula is: I 1 – 1½ II 1 – 2 III 1½ – 3½ IV 3½ – 2½ V. The toe tips are expanded into small disks with circummarginal grooves. The relative length of toes is: IV > III > V > II > I. The feet possess prominent and translucent subarticular tubercles: one each on digits I and II, two each on digits III and V, and three on digit IV. The inner metatarsal tubercle is prominent, raised, and translucent, while the outer metatarsal tubercle is absent (Quah et al. 2017).

When A. nazgul was described, only one other Abavorana species was known. Abavorana nazgul can be distinguished from A. luctuosa populations from Peninsular Malaysia by the following ways: A. nazgul has a black dorsum while A. luctuosa has orange/reddish-brown; the dorsolateral stripes in A. luctuosa are white or cream; spots on A. luctuosa are either absent or only faintly present at the corner of the jaws and along the flanks; A. luctuosa has fine white or grayish-blue spots or bars on the upper surfaces of its limbs; the underside of A. luctuosa is immaculate, or occasionally shows inconspicuous spots or reticulations on the belly and the underside of the thighs; A. luctuosa adult males are on average smaller (42.7 – 44.5 mm snout-vent length) than A. nazgul males (Quah et al. 2017).

Differences between A. nazgul and A. luctuosa populations from Borneo are similar to that between A. nazgul and A. luctuosa from Peninsular Malaysia, but the Bornean A. luctuosa populations show bold, cream-colored bars under the limbs. Male A. luctuosa individuals from Borneo are larger (53.0 – 58.8 mm snout-vent length) than A. nazgul males. Female A. luctuosa have been reported to be larger (53.0 – 60.0 mm snout-vent length) than the single female A. nazgul (52.8 mm snout-vent length) examined so far (Quah et al. 2017).

Abavorana nazgul can be differentiated from the related Pulchrana picturata species complex by the fact that members of the P. picturata complex have fine or warty textured dorsolateral lines that are more poorly developed, a well-developed rictal ridge, large outer metatarsal tubercles (as opposed to none), and humeral glands on the anteroventral (rather than the ventral) surface of the brachium. Abavorana nazgul can be further distinguished from the similarly patterned P. centropeninsularis by the latter’s black unmarked dorsum without faint orange speckles, smaller adult male body size (37.4 – 37.6 mm snout-vent length), bright vermillion dorsolateral stripes, larger humeral gland, supernumerary tubercles at the base of the first phalanx on each finger, and a lower recorded elevation range (90 – 105 m) (Quah et al. 2017).

In life, Abavorana nazgul is black overall with orange dorsolateral stripes extending from the rostrum, along the canthus, the eyelids, and the dorsolateral part of the body, before stopping at the sacrum, where it almost forms a complete loop. The stripes are connected at the rostrum, and the color is more yellowish-orange. A series of faint orange specks runs along the center of the dorsum. On the lower flanks of the body, the color transitions from black to dark-gray. The underside is gray-brown. Creamy yellow spots are present on the flanks, the dorsal side of limbs, and along the upper lip passing beneath the tympanum towards the corner of the jaw. Some of these cream spots, especially those on the hind limbs, elongate into short bars. On the underside, the spots are whitish. The spots on the ventral surfaces of the thighs are smaller than those on the throat and the belly. In preservative, the black fades to dark-gray, while the orange dorsolateral stripe and creamy yellow spots/bars all turn cream. The lower flanks and digits are a lighter shade of grey that turns gray-brown as it travels to the underside. The spots on the ventrum remain whitish (Quah et al. 2017).

The dorsolateral stripes running along the body can be yellow, instead of orange. The stripe across the snout can also be discontinuous. Some individuals possess a small, round, and indistinct outer metatarsal tubercle. Juveniles have fewer creamy yellow spots on the flanks; they also lack spots at the upper labial margin. The stripes across the snout and along the dorsolateral margins of the body are bright orange or vermilion in juveniles. In a female specimen, the skin texture near the vent and on the back of the thigh is more rugose or wrinkly than in males. The female specimen is also slightly larger than the males (Quah et al. 2017).

Abavorana nazgul is only known from the mountain, Gunung Jerai, in the state of Kedah on the west coast of Peninsular Malaysia. It is associated with riparian habitats, and can be found near streams. It has been only been found at elevations between 800 – 1200 m (Quah et al. 2017).

Life History, Abundance, Activity, and Special BehaviorsAbavorana nazgul can be found in riparian habitats, in the vicinity of streams. At night, it hides in the leaf litter, vegetation, tangled roots, or overhanging banks along streams (Quah et al. 2017).

Males produce a distinctive “mew”-like call, and can be heard calling from stream banks, sometimes hidden in crevices or among plant roots (Quah et al. 2017).

Breeding season occurs during the dry season between the months of November and March. During the breeding season, tadpoles can be found in deep, open, and sediment-laden pools along creeks. Recently emerged juvenile frogs have been found in April (Quah et al. 2017).

Abavorana nazgul belongs to the family Ranidae. It was previously thought to be a highland melanistic form of A. luctuosa. However, phylogenetic analysis (Bayesian Inference and Maximum Likelihood) of mitochondrial genes 16s and ND1, as well as three tRNAs (tRNA-leu, tRNA-lle, and tRNA-gln), revealed that A. nazgul is sister to A. luctuosa populations from Peninsular Malaysia and Sipitang, Sabah. The two sister lineages are further found to be sister to a presumed A. luctuosa sampled from Lahad Datu, Sabah (Quah et al. 2017).

The species epithet nazgul is a reference to the “Nazgûl” in J. R. R. Tolkien’s The Lord of the Rings. In the story, the Nazgûl were ghostly figures that wore black cloaks. The frog is named after them because of its black coloration (Quah et al. 2017).

Prior to the description of A. nazgul, the genus Abavorana was composed of only one widespread species, A. luctuosa. However, findings from the phylogenetic analysis of A. nazgul indicate that A. luctuosa may be a species complex with more species to be described (Quah et al. 2017).

Gunung Jerai, the mountain in which A. nazgul is found, is the home of at least one other herptofauna endemic. This is thought to be because Gunung Jerai is geographically isolated from other mountain systems and has been a land-bridge island multiple times over geological time, allowing for species isolation and evolution (Quah et al. 2017).